Studies on the cytotoxic activity of human lymphocytes. II. Interactions between IgG and Fc receptors leading to inhibition of K cell function.

The inhibition of human K cell-mediated cytolysis by a variety of immunoglobulin preparations was studied. It was found that inhibition was not a simple function of IgG concentration but was dependent on the mode of immunoglobulin presentation. The relative inhibitory capacity of IgG preparations on a weight basis was as follows: cell associated Ig larger than or equal to immobilized immune complexes greater than insoluble immune complexes greater than soluble immune complexes greater than heat-aggregated Ig greater than monomeric Ig. These results imply that the inhibitory capacity of immunoglobulin is determined by ligand (Fc) multivalency. It was found that although interactions between immunoglobulin and Fc receptors occur at low temperatures, these interactions lead neither to lysis nor to K cell inactivation. A temperature-sensitive post-binding event was required both for lysis to occur and for K cells to be inactivated. These findings lead us to propose that an IgG-induced redistribution ("capping") of Fc receptors on the K cell surface may be required for cytolysis and for effector -ell inactivation.